Inductance

Electro Magnetic Field - EMF - induced into a circuit

Inductance is the property of a circuit when there is an electro magnetic field - EMF - induced into the circuit by the change of flux linkages produced by a current change.

The unit of inductance is henry - H - where a circuit has an inductance of one henry when an e.m.f. of one volt is induced by a current changing at the rate of one ampere per second.

Induced electromagnetic field - EMF - in a coil can be expressed as

E = -n dΦ / dt         (1)

where

E = electromagnetic field - EMF (Volts)

n = turns

dΦ = change in flux (Webers, Wb)

dt = time (s)

Alternatively, induced electromagnetic field - EMF - in a coil of inductance L henrys can be expressed as

E = -L dI / dt         (2)

where

L = inductance (henrys, H)

dI = change in current (Amperes)

dt = time (s)

Example - Inductance

The EMF induced in a coil with 500 turns with a change of flux of 30 mWb in 30 ms can be calculated as

E = -500 (30 10-3 Wb) / (30 10-3 s) 

    = -500 Volts

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